Local and global planarization of semiconductor wafers becomes increasingly important as more metal layers and interlayer dielectric layers are stacked on the wafers. A preferred method to planarize semiconductor wafers is the chemical mechanical polishing (CMP) method, where a surface of a semiconductor wafer is polished using a slurry solution supplied between the wafer and a polishing pad. The CMP method is also widely used for damascene process to form copper structures on the semiconductor wafers.
In general, a CMP equipment includes a polishing table where a polishing pad is placed and a wafer carrier that supports a semiconductor wafer and presses the wafer against the polishing pad. One of the most important performances of a CMP equipment is productivity. For higher productivity, a CMP equipment typically requires more polishing tables and more wafer carriers. In order to use more polishing tables and more wafer carriers efficiently, it is important to transfer the semiconductor wafers to and from the wafer carriers efficiently so that the wafer carriers can receive fresh wafers with least amount of idle time after they unload polished wafers. The reduced idle time of the wafer carriers contributes to high productivity of the CMP equipment.
In view of these issues, what is needed is an apparatus and method for polishing semiconductor wafer with highly efficient wafer transfer devices.